1. Field of the Invention
Fiber reinforced resin composite structures are used in the manufacture of parts and finished goods in a wide variety of applications, e.g., automotive, recreation vehicle, trucking, aerospace, marine, rail, appliance, athletic equipment, container, construction, anti-corrosion, electrical and medical industries. The present invention relates generally to open or closed molded resin infusion and resin transfer molding techniques for the production of fiber reinforced resin plastic (composite) structures in these and other industries.
More specifically it relates to and provides for the use of interlaminar three-dimensional spacer fabrics in vacuum-induced resin infusion and resin transfer molding processing of fiber reinforced plastics as part of or all of the composite laminate. The spacer fabric used according to this invention acts as an Interlaminar Infusion Medium that significantly improves the speed (by 200% to 400%), uniformity and ability to quality-control the transfer, delivery and distribution of a liquid matrix resin (plastic) throughout the laminate stack with utility far beyond any other product or process in prior art or on the market, as well as providing a reinforcing composite lamina that dramatically improves mechanical and structural properties in the finished composite part. Thereby, the manufacture of parts and finished goods is facilitated in a wide range of industries.
2. General Description of the Prior Art
Prior Art Open Molded Laminating Techniques
A typical open mold process for constructing composite parts generally includes the laying or placing of either dry fibers or previously resin-impregnated fibers (also known as “pre-pregs”) into an open mold of a desired shape. Dry fiber reinforcements that have been saturated with liquid resin using manual surface-applied techniques such as hand wet-out or spray application (processes commonly referred to as hand/contact lay-up and spray lay-up, respectively), are then allowed to cure to form the composite product. Once placed in the open mold, pre-pregs are sometimes simply allowed to cure to form. When a flexible vacuum bag is applied to the part during the curing stage of these traditional open molding processes, ambient atmospheric pressure can provide an improvement in the consolidation of the laminate prior to curing. This modification is sometimes referred to as “wet-preg vacuum bagging”.
Benefits and Drawbacks of Prior Art Open Molded Laminating Methods
Open mold processing has relatively low start-up and implementation costs for limited-run or custom part production. However, the problems associated with open mold processing include: high emissions of volatile organic compounds; uneven distribution of resin within the fiber structure often resulting in over-saturated and/or under-saturated areas; the formation of air voids and bubbles; and commonly the use of excess resin or waste of resin in the process. Furthermore, open molding unit production costs are relatively high due to the labor-intensive and limited throughput.
Prior Art Closed Molded Resin Infusion Techniques
In closed mold processing, fiber and/or other reinforcement structures, collectively referred to herein as the “pre-form,” are cut to fit then placed in the mold. A method of enclosing and compressing the pre-form against and within the mold is then employed. Resin is introduced into the pre-form by entry ports through the enclosure. Following at least a partial curing of the resin, the enclosure is first removed, followed by the finished part. There are two principal closed molded resin infusion techniques commonly used to enclose and compress the pre-form against the mold, and to distribute resin through the pre-form, as follows:
Vacuum Infusion employs one generally rigid mold component and a flexible bag or membrane that when joined together are sealed to form a “closed” mold. Typically before applying the flexible bag or membrane a disposable barrier layer commonly referred to as a peel ply is placed on top of the pre-form. A peel ply allows resin to pass through it but will not stick to the ultimately cured resin. A disposable infusion medium and/or perforated injection tubing is then placed on top of the peel ply to aid in the delivery and distribution of the liquid resin down through the laminate stack. In the case of a reusable vacuum bag or membrane the distribution channels may be incorporated into the bag. Vacuum pressure is then applied and draws resin through feed-lines into the mold and through the fiber pre-form. This technique is commonly referred to as surface vacuum infusion processing since the resin is introduced at the top surface of the laminate assembly. Examples are described in Seeman et al. U.S. Pat Nos. 5,052,906, 4,902,215 and 5,601,852.
Resin Transfer Molding, on the other hand, employs two generally rigid mold components, that when mated together and sealed form an interior cavity into which liquid resin is introduced. The resin may be introduced either with or without the aid of vacuum or applied pressure.
Combinations and variations of vacuum infusion, resin transfer molding and other techniques can also be employed and are well known to those familiar with the state of the art of composite production.
Benefits and Drawbacks of Prior Art in Closed Molded Resin Infusion
A number of benefits can be derived through the use of vacuum infusion vis-à-vis open molding and resin transfer molding techniques. As compared to open molding, labor requirements can be reduced and the rate of production from each mold can be improved. For example, the labor involved in rolling out air bubbles and distributing the resin is reduced since the applied vacuum improves the distribution of resin throughout the pre-form. Vacuum infusion also helps to maintain more consistent resin-to-fiber ratios by providing the fabricator with the ability to control more precisely the resin input. Product quality and strength are improved since the vacuum removes trapped air and serves to insure tight bonding of all materials in the lay-up. Compared to resin transfer molding, vacuum infusion generally requires less set-up time and has much lower tooling costs. Additionally, resin transfer molding has the inherent risk of fiber washout or fiber movement/displacement due to resin flow, as well as resin racing or non-wetting in areas of complexity or varying part thickness.
The greatest drawback of surface vacuum infusion is the high waste and nonprofit stream costs in the disposal of peel plies and surface infusion media. Surface vacuum infusion also has an inherent risk of resin pooling in low-lying areas due to loss of vacuum pressure after the passage of the resin flow front.
In view of the foregoing disadvantages inherent in the known types of resin infusion techniques now present in the prior art, the present invention provides a new technique for resin infusion through the novel use of Three-Dimensional Spacer Fabric Interlaminar Infusion Media and Reinforcing Composite Lamina in the laminae.
The use of Three-Dimensional Spacer Fabric Interlaminar Infusion Media in a reinforcing composite lamina to aid in the transfer, delivery and distribution of resin according to the present invention substantially departs from the conventional concepts and designs of the prior art. In so doing, a technique and a material is provided for significantly increasing the resin distribution rate and uniformity throughout the laminae while also improving the mechanical properties of the finished cured product.
Object of the Invention
A basic object of the present invention is to provide for the three-dimensional spacer fabric interlaminar resin infusion media and in a reinforcing composite lamina that will overcome the shortcomings of the prior art methodology.
An object of the present invention is to provide three-dimensional spacer fabric interlaminar resin infusion media and reinforcing composite laminate structures for wide use in vacuum-induced resin infusion processes for composite manufacturing.
Another object is to provide for the use of three-dimensional spacer fabric resin infusion media and reinforcing composite lamina for the improvement of vacuum-induced resin infusion rates.
Another object is to provide three-dimensional spacer fabric resin infusion media and reinforcing composite lamina for improvement in the uniformity properties of vacuum-induced laminates.
Other objects and advantages of the present invention will be apparent from the following description, and when considered in conjunction with the accompanying drawings and claims for the scope of the present invention.
To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, it being understood, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated.